Those are just a few minor complaints. You could really simplify this and cut about 130 lines off of it (maybe even more). Focus on writing applications that your dog would be able to use and understand. Typing something like 5 * 5 is much better than having to select from a menu then enter the amount of number you would like to add.

I would usually complain about calling system system("CLS"), but I have found myself doing it before so I'll cut you some slack. Just remember, calling system leaves a huge security hole in your program, is very resourceful, and leaves your program 'grounded' to a specific OS.

Essentially, to be able to make calculations based on something like this:

9(1 + 6)

you'll have to parse the user's input to basically separate the numbers from the operators and translate them into something that your program can calculate an output for. You'll want to find tutorials about parsing/splitting strings for this. The amount of work for this really depends on how interpretive of human typing you want your calculator to be. Like, are these: 9 (1 + 6) and 9(1+6) valid inputs ? or will only this one work: 9*(1+6) ?

To start with, instead of using an integer like

whatoperation

you would start with accepting a full string as an input. Try it with the simplest case first like accepting only 2+3 from from the user into a string and then parse it and calculate then print the output " = 5".

Then eventually u could expand it to accept an arbitrary number of operations on the same line: 3/4 +6(1/4+2^3) - sqrt(4/(2pi))

As far as adding more operations to your calculator there's lots ! Like square root, exponents, logarithms, factorials, combinations/permutations - maybe even a prime number detector/factor'er'